1. The problem asks which scientist(s) conducted experiments involving injecting mice with S bacteria and R bacteria. 2. This is a historical biology question related to the discovery of the transforming principle in genetics. 3. The key experiment was performed by Frederick Griffith in 1928, where he injected mice with two strains of pneumococcus bacteria: the virulent S strain (smooth) and the non-virulent R strain (rough). 4. Griffith observed that mice injected with heat-killed S bacteria and live R bacteria died, indicating that some "transforming principle" from the dead S bacteria converted R bacteria into virulent S bacteria. 5. Therefore, the correct answer is Griffith. 6. The other scientists listed (Watson & Crick, Avery, Hershey & Chase) contributed to DNA structure discovery and DNA as genetic material but did not perform the S and R bacteria mouse injection experiments. Final answer: Griffith